| Nanofibrilled cellulose(NFC) is made of depolymerized cellulose by mechanical, chemical and biological process. Compared with the traditional cellulose and microcrystalline cellulose, the surface area, swelling capacity of NFC are higher, and a large number of the hydroxyl groups on the surface of NFC are active, all of these will be beneficial for its functional modification to prepare the novel dietary fiber. But now the use of toxic and harmful ingrendients in the process of preparing NFC made is difficult to use in food. Thus it is particularly urgent to find an eco-friendly method to prepare NFC. The components of secondary wall, such as cellulose, hemicellulose, and lignin, show discontinuous layer structure, and bond to each other. The main bottleneck of preparing NFC is to extract and depolymerize cellulose. At present, the main method to prepare NFC is based on acid-or alkaline hydrolysis and high strength mechanical treatment, which has large energy consumption and serious environmental pollution. In this study, high density steam flash-explosion(HDSF) as an innovative pretreatment of biomass was firstly employed to destroy and depolymerize the structure of rice straw, and the NFC was prepared. Then the properties of NFC as dietary fiber were studied. The specific results were as follows:Firstly, after HDSF treatment, the content of hemicellulose and lignin decreased, the content of cellulose increased and the rice straw was depolymerized. As the pressure increased, the trend was more prominent. The infrared spectrum, X-ray diffraction and thermogravimetric analysis showed that after HDSF treatment the chemical composition and crystalline structure of rice straw wasn‘t changed, but compared with raw rice straw, the crystallinity index(CI) increased. In general, after treated with 1.6 MPa and 270 s, the rice straw was depolymerized to smooth fiber with 10 μm, and shows the much lower CI(54.81%). So the 1.6 MPa treated rice straw was choose to prepare NFC. The diameter of NFC was 30~200 nm, and its length can be up to a few microns. The total dietary fiber content was 85.86%.Secondly, in order to enchance the ability of NFC to adsorb oil, the NFC was esterificated with octenylsuccinic anhydride(OSA), and the physicochemical properties of NFC, OSA-NFC were determined. We found that the swelling capacity(SWC), apparent viscosity(5%) and the capacity of binding bile acids or cholesterol of NFC, which was 99.75 m L/g、1544 m Pa?s、7.96 μmol/100 mg、37.57 mg/g(p H7.0) respectively, were much higher than the wheat insoluble dietary fiber(WDF). Furthermore, compared with NFC, the water retention capacity(WRC) and SWC of OSA-NFC decreased, but its oil holding capacity(OHC), apparent viscosity, the capacity of binding bile acids and cholesterol, scavenging capacity towards NO2- increased, and this trend was more outstanding with the increase of DS.Finally, the OHC of NFC and OSA-NFC in simulated digestion experiment were determined, when they were used as dietary fiber supplements and food additives. And the results showed that in both cases, the OHC of dietary fiber enhanced with the content and DS increased, and with the same concentration of NFC and OSA-NFC the OHC were similar. In addition, the properties of sausage were measured after added NFC, OSA-NFC or WDF. And the result showed that the colour, springiness and cohesiveness of the sausage changed little, but the content of water increased, the hardness and chewiness decreased. And compared with the sausages which were added WDF, the properties of sausages added NFC and OSA-NFC were much batter. But when the content of dietary fiber was 1% and 2%, the sensory evaluation scores of sausage almost had no difference. |
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